Ophthalmic lens with multiple phase plates

ABSTRACT

An ophthalmic lens for providing a plurality of foci has an optic including an anterior surface, a posterior surface, and an optical axis. The ophthalmic lens further includes a central phase plate, an intermediate phase plate surrounding the central phase plate, and an outer refractive region. The central phase plate comprises a first base curvature having a first radius of curvature and is configured such that the lens is able to direct light to a first focus and a second focus corresponding different diffraction orders of the phase plate. The intermediate phase plate is configured to change the overall resultant distribution of light directed to the second focus. The outer refractive region has no diffractive optical power and surrounds the intermediate phase plate. The outer refractive region is configured to direct light to the second focus and has an aspheric shape configured to reduce an optical aberration.

This application is a continuation of, and claims prior to, U.S. patentapplication Ser. No. 11/259,534, filed Oct. 25, 2005, now U.S. Pat. No.7,455,404, the entire contents of which is hereby incorporated byreference in its entirety for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an ophthalmic lens, and morespecifically to multifocal ophthalmic lenses that combine bothrefraction and diffraction to provide an ocular image.

2. Description of the Related Art

Ophthalmic lenses, such as intraocular lenses (IOLs), phakic IOLs, andcorneal implants, are used to enhance ocular vision. For instance, IOLsare now routinely used to replace the natural lens of an eye that isremoved during cataract surgery. More recently, diffractive IOLs havebeen advantageously used to reduce lens thickness and correct forpresbyopia. For instance, diffractive bifocal lenses divide incidentlight into two diffractive orders to provide both near and distancevision. The use of diffractive optics in ophthalmic lenses is describedby Cohen in U.S. Pat. Nos. 4,881,804; 4,881,805; 4,995,714; 4,995,715;5,017,000; 5,054,905; 5,056,908; 5,117,306; 5,120,120; 5,121,979;5,121,980; and 5,144,483, which are all herein incorporated byreference. Freeman also describes the use of diffractive optics inophthalmic lenses in U.S. Pat. Nos. 4,637,697; 4,641,934; 4,642,112;4,655,565; and 5,748,282, which are also herein incorporated byreference.

In such lenses, the optic area is generally divided into a plurality ofannular zones or echelettes that are offset parallel to the optical axisby predetermined step heights to provide a specific phase relationshipbetween the zones. The term “zone plate” or “phase plate,” as usedherein and as is generally recognized in the art, is defined to be apattern of concentrically arranged annular zones which is characterized,at least in part, by the step height between zones, the circumferentialspacing between zones, and the surface profile of each zone. Zone platesare usually configured to maintain a predefined phase relationship oflight passing through the zones. In addition to Cohen and Freeman,Futhey also describes various ophthalmic diffractive lenses, forexample, in U.S. Pat. Nos. 4,936,666; 5,129,718; and 5,229,797, hereinincorporated by reference.

In one approach, a phase plate or zone plate comprises a plurality ofzones in which the optical height of the steps (i.e., the physicalheight times the difference between the refractive index of the materialand the refractive index of the surrounding media) between theindividual zones is one-half that of light at a design wavelength in thevisible range. In such designs, approximately 80% of the light at thedesign wavelength is evenly split between zeroth and first diffractionorders, where the zeroth diffraction order is generally considered to belight that is un-diffracted or unaffected by the zone plate. This zoneplate configuration is used to produce a bifocal lens in which (1) thezeroth diffraction order produces a first focus or focal point fordistant vision and (2) the first diffraction order produces a secondfocus or focal point corresponding to near or intermediate vision. Inaddition, chromatic dispersion produced by the first diffraction order,which is usually opposite in sign to refractive chromatic dispersion,may be used to reduce the overall chromatic aberrations in the nearvision focus, since the refractive and diffractive chromatic dispersionscomponents tend to cancel one another. However, the distant vision focusdoes not benefit from this diffractive chromatic dispersion, since itcomprises only light that is un-diffracted by the zone plate. Thus, thedistance vision is purely refractive and receives no reduction in anychromatic aberrations induced by refractive chromatic dispersions.

A characteristic of ophthalmic lenses incorporating diffractive zones orphase plates is that the amount of light in the near and distant foci issubstantially constant for all pupil sizes. It is desirable in certaininstances to increase the amount of light in the distant focus as thepupil size increases, for instance under intermediate or low lightconditions. One way to increase the amount of light dedicated todistance vision is to restrict the zone plate to the central portion ofthe lens and to make the outer region of the lens refractive only, asdisclosed in Cohen '804. Another approach is disclosed by Lee et al. inU.S. Pat. No. 5,699,142, herein incorporated by reference. Lee et al.teaches a diffractive lens comprising an apodization zone in which thestep height between zones in the transition region is progressivelyreduced. The steps between zones are centered on a base curve BC so asto avoid sharp discontinuities in the resulting wavefront that canproduce unwanted diffractive effects. In either of these designs, theouter refractive portion of the lens does not benefit from the use ofdiffractive power to reduce chromatic aberrations, potentially resultingin increased chromatic aberrations as the pupil size increases underlower lighting conditions.

One problem associated with multifocal/bifocal IOLs is the problem ofhalos. This problem manifests itself when light from the unused focalimage creates an out-of-focus image that is superimposed on the usedfocal image. For example, if light from a distant point source orslightly extended source is imaged onto the retina of the eye by thedistant focus produced by a bifocal IOL, the near focus produced by theIOL will simultaneously superimpose a defocused image on top of theimage formed by the IOL's distant focus. This defocused image maymanifest itself in the form of a ring of light surrounding the in-focusimage produced by the IOL's distant focus.

Devices and method are needed to improve the performance of diffractivelenses in ophthalmic applications.

SUMMARY OF THE INVENTION

One aspect of the present invention involves an ophthalmic lenscomprising an optic having an anterior surface, a posterior surface, andan optical axis. The ophthalmic lens further comprises a first regionhaving a first optical power and a second region having a second opticalpower. The first region comprises a multifocal phase plate configuredfor forming a first focus and a second focus, while the second regioncomprises a monofocal phase plate for forming a third focus. Themonofocal phase plate and the multifocal phase plate are preferablydisposed about at least one base curvature. In certain embodiments, thefirst region comprises a first base curvature having a finite firstradius of curvature and the second region comprises a second basecurvature having a finite second radius of curvature different from thefirst radius of curvature. The ophthalmic lens may further comprise athird region having a third optical power and comprising a third phaseplate. For example, the third region may be an intermediate region thatis disposed between the monofocal phase plate and the multifocal phaseplate.

In one embodiment the first region is disposed in the center of theoptic and the second region is disposed outside the first region.Alternatively, the second region is disposed in the center of the opticand the first region is disposed outside the second region. In eitherembodiment, the base curvature may have a shape that is spherical,parabolic, elliptical, hyperbolic, or some other aspherical shape. Thefirst region may have a refractive optical power that is preferablygreater than a diffractive optical power of the multifocal phase plateand the second region may have a refractive optical power that ispreferably greater than a diffractive optical power of the monofocalphase plate.

The monofocal phase plate and the multifocal phase plate may both bedisposed on the anterior surface of the optic or on the posteriorsurface of the optic. Alternatively, the monofocal phase plate and themultifocal phase plate may be disposed on opposite surfaces of theoptic.

In another aspect of the invention, at least one of the multifocal phaseplate and the monofocal phase plate comprises a plurality of concentriczones and a step along the optical axis between adjacent zones.Alternatively, at least one of the multifocal phase plate and themonofocal phase plate has a variation in refractive index across thesurfaces thereof. Preferably, the variation in refractive index acrossthe surfaces is in a radial direction from the center of the optic,although other configurations are also possible. Such a variation inrefractive index may be produced, for instance, by a phase hologram.

The multifocal phase plate may be a bifocal phase plate such as a MOD0.5 phase plate or MOD 1.5 phase plate or, more generally, a MOD x.5phase plate, where x is an integer. The monofocal phase plate may be aMOD 1 phase plate, a MOD 2 phase plate or, more generally, a MOD y.0phase plate, where y is an integer. Other types of phase plates may alsobe used that, for example, produce one or more negative diffractionorders.

In a particularly useful aspect of the invention, the first regioncomprises a first base curvature having a first radius of curvature andthe second region comprises a second base curvature having a secondradius of curvature, the first radius of curvature being different fromthe second radius of curvature. Additionally, the multifocal phase platemay be a MOD 0.5 phase plate and monofocal phase plate may be a MOD 1phase plate. In this configuration, the first focus corresponds to azeroth diffraction order of the multifocal phase plate, the second focuscorresponds to a first diffraction order of the multifocal phase plate,and the third focus corresponds to a first diffraction order of themonofocal phase plate.

The first focus may be used to provide distant vision and the secondfocus may be used to provide near vision or intermediate vision. Thesecond base curvature may be configured such that the third focus isdisposed at substantially the same location as either the first focus,the second focus, between the first and second focus, or some otherlocation that is different from either the first or second focus. Eitheror both of the multifocal phase plate and the monofocal phase plate maybe adapted to adjust chromatic aberrations in the second and/or thirdfoci. Similarly, the monofocal phase plate, the second base curvature,or both may be configured to reduce spherical or other aberrationsproduced by first region in at least one of the first focus and thesecond focus.

In an additional aspect of the invention, an ophthalmic lens comprisesan optic having an anterior surface, a posterior surface, and an opticalaxis, a first region and a second region. The first region comprises afirst phase plate disposed on a first base curvature with a finite firstradius of curvature. The second region comprising a second phase platedisposed on a second base curvature with a finite second radius ofcurvature. In addition, the first radius of curvature may be differentfrom the second radius of curvature.

In another aspect of the present invention, an ophthalmic lens comprisesan optic having an anterior surface, a posterior surface, and an opticalaxis. The ophthalmic lens further comprises a first region having afirst refractive optical power, where the first region comprises (1) afirst base curvature having a first radius of curvature and (2) amultifocal phase plate for forming a first focus and a second focusdisposed closer to the optic than the first focus. The ophthalmic lensalso comprises a second region having a second refractive optical power,where the second region comprises (1) a second base curvature having asecond radius of curvature different from the first radius of curvatureand (2) a monofocal phase plate for forming a third focus. Preferably,the first radius of curvature and the second radius of curvatures areboth finite so that the first region and the second region both haverefractive optical power.

In yet another aspect of the present invention, an ophthalmic lenscomprises an optic having an anterior surface, a posterior surface, andan optical axis. The ophthalmic lens further comprises a first regionhaving a first refractive optical power, the first region comprising amultifocal phase plate disposed on a first base curvature having a firstradius of curvature. The ophthalmic lens also comprises a second regionhaving a second refractive optical power, the second region comprising amonofocal phase plate disposed on a second base curvature having afinite second radius of curvature different from the first radius ofcurvature. Preferably, the first radius of curvature and the secondradius of curvatures are both finite so that the first region and thesecond region both have refractive optical power.

In one aspect of the present invention, an ophthalmic lens comprises anoptic having an anterior surface, a posterior surface, a first basecurvature, and an optical axis. The ophthalmic lens further comprises amultifocal phase plate configured to direct light to a first focus and asecond focus, the multifocal phase plate comprising a first plurality ofechelettes centered about a first base curvature in a direction that isparallel to the optical axis, the first base curvature having a firstradius of curvature. The ophthalmic lens also comprises an intermediatephase plate surrounding the multifocal phase plate and configured tochange the overall resultant amplitude and/or distribution of lightdirected to the second focus, the intermediate phase plate comprising asecond plurality of echelettes centered about the first base curvatureor about a second base curvature having a second radius of curvaturedifferent from the first radius of curvature. The ophthalmic lensadditionally comprises an outer refractive region having a refractiveoptical power and no diffractive optical power, the outer refractiveregion surrounding the intermediate phase plate and configured to directlight to the first focus.

In some embodiments, the first plurality of echelettes comprises a firststep height between adjacent echelettes the second plurality ofechelettes comprises a second step height between adjacent echelettes.The second step height may be less than the first step height. Incertain embodiments, the first step height is determine by the equation0.5×λ/(n2−n1) and the second step height is determine by the equationB×λ/(n2−n1), where:

B is a constant,

λ is a design wavelength,

n2 is the refractive index of the ophthalmic lens,

n1 is the refractive index of the media adjacent the phase plates.

wherein B may be about 0.25, about 0.75, or some other value greaterthan or less than 1. In one embodiment the second plurality ofechelettes comprises 4 echelettes, although any number of echelettes maybe used. In other embodiment, second plurality of echelettes maycomprise a first step height between one or more adjacent echelettes anda second step height between one or more adjacent echelettes. In suchembodiments, the first step height may be determined by the equation0.375×λ/(n2−n1), and the second step height is determined by theequation 0.125×λ/(n2−n1).

In yet another aspect of the present invention, an ophthalmic lenscomprises an optic having an anterior surface, a posterior surface, andan optical axis. The ophthalmic lens further comprises a multifocalphase plate, a monofocal phase plate, an intermediate phase platelocated between the multifocal phase plate and the monofocal phaseplate. The multifocal phase plate may be configured to direct light to afirst focus and a second focus. The multifocal phase plate furthercomprises a first plurality of echelettes disposed on a first basecurvature having a first radius of curvature. The monofocal phase platecomprise a second plurality of echelettes disposed on a second basecurvature having a second radius of curvature different from the firstradius of curvature. The intermediate phase plate comprises a thirdplurality of echelettes disposed on a third base curvature having athird radius of curvature and configured to change the overall resultantamplitude and/or distribution of light directed to the second focus.

The third radius of curvature of the ophthalmic lens may equal to thefirst radius of curvature or may be greater than or less than the firstradius of curvature. The multifocal phase plate and the intermediatephase plates generally produce a halo image in a plane containing thefirst focus.

In certain embodiments, the first plurality of echelettes comprise afirst step height between adjacent echelettes and the second pluralityof echelettes comprises a second step height between adjacentechelettes. The second step height may be less than the first stepheight. The first step height may be determine by the equation0.5×λ/(n2−n1) and the second step height may be determine by theequation B×λ/(n2−n1), where:

B is a constant,

λ is a design wavelength,

n2 is the refractive index of the ophthalmic lens,

n1 is the refractive index of the media adjacent the phase plates.

wherein B may be about 0.25, about 0.75, or some other value greaterthan or less than 1. In one embodiment the second plurality ofechelettes comprises 4 echelettes, although any number of echelettes maybe used. In certain embodiments, the second plurality of echelettescomprises a first step height between one or more adjacent echelettesand a second step height between one or more adjacent echelettes. Insuch embodiments, the first step height is determined by the equation0.375×λ/(n2−n1), and the second step height is determined by theequation 0.125×λ/(n2−n1). In other embodiments, the first plurality ofechelettes comprises a first step height between adjacent echelettes thesecond plurality of echelettes comprises a plurality of different stepheights between adjacent echelettes and the plurality of different stepheights each are less than the first step height. Alternatively, theplurality of different step heights progressively decrease as thedistance from the optical axis increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention may be better understood from thefollowing detailed description when read in conjunction with theaccompanying drawings. Such embodiments, which are for illustrativepurposes only, depict the novel and non-obvious aspects of theinvention. The drawings include the following 19 figures, with likenumerals indicating like parts:

FIG. 1 is a side view of a prior art bifocal intraocular lensillustrating how light from a distant object is focused onto the retinaof an eye.

FIG. 2 is a side view of a prior art bifocal intraocular lensillustrating how light from a near point source object is focused ontothe retina of an eye.

FIG. 3 is a side view of one embodiment of a diffractive ophthalmic lensaccording to the invention comprising a plurality of diffractive phaseplates, wherein a peripheral phase plate is configured to providedistant vision.

FIG. 4 is a side view of a second embodiment of a diffractive ophthalmiclens comprising a plurality of diffractive phase plates, wherein aperipheral phase plate is configured to provide near or intermediatevision.

FIG. 5 is a side view of a third embodiment of a diffractive ophthalmiclens comprising a plurality of diffractive phase plates producingprimarily two diffraction orders, wherein a peripheral phase plate isconfigured to provide near or intermediate vision.

FIG. 6 is a side view of a fourth embodiment of a diffractive ophthalmiclens comprising a plurality of diffractive phase plates producingprimarily two diffraction orders, wherein a peripheral phase plate isconfigured to provide distant vision.

FIG. 7 is a side view of a fifth embodiment of a diffractive ophthalmiclens comprising a plurality of diffractive phase plates producingprimarily two diffraction orders, wherein the peripheral phase plate isconfigured to provide a focus or focal point that is disposed betweenthe foci produced by the central phase plate.

FIG. 8 is a side view of a sixth embodiment of a diffractive ophthalmiclens comprising three diffractive phase plates.

FIG. 9 is a side view of a eighth embodiment of a diffractive ophthalmiclens comprising two phase plates, each phase plate disposed on adifferent, finite radius of curvature.

FIG. 10 is a side view of the ninth embodiment of a diffractiveophthalmic lens comprising an intermediate phase plate disposed betweena bifocal phase plate and a monofocal phase plate.

FIG. 11 is the diffractive ophthalmic lens shown in FIG. 10 showingincident ray impinging the outer peripheries of the intermediate phaseplate, bifocal phase plate, and monofocal phase plate.

FIG. 12 is a front view of an image plane disposed at one of the focusesproduced by the diffractive ophthalmic lens illustrated in FIG. 10.

FIG. 13 is a graphical representation of intensity profiles along thecross-section 13-13 in FIG. 12.

FIG. 14 is a graphical representation of the intensity distributionlight along the cross-section 13-13 shown in FIG. 12 including physicaloptics effects.

FIG. 15 is a graphical representation of the intensity distributionlight along the cross-section 13-13 shown in FIG. 12 showing thesummation of the various components illustrated in FIG. 14.

FIG. 16 is a graphical representation of the intensity distributionlight for an ophthalmic lens not containing an intermediate phase plate.

FIG. 17 is an embodiment of an ophthalmic lens according to the presentinvention illustrating the profile of the echelette in an intermediatephase plate, bifocal phase plate, and monofocal phase plate.

FIG. 18 is a side view of the tenth embodiment of a diffractiveophthalmic lens comprising an intermediate phase plate disposed betweena bifocal phase plate and a refractive region.

FIG. 19 is an embodiment of an ophthalmic lens according to the presentinvention illustrating the profile of the echelette in an intermediatephase plate, bifocal phase plate, and refractive region.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present inventions are directed to a multifocalophthalmic lens (e.g., an intraocular lens (IOL), phallic IOL, andcorneal implant) comprising a plurality of surface regions having both arefractive optical power and a diffractive optical power that togetherprovide enhanced ocular vision. The terms “power” or “optical power”, asused herein, mean the ability of a lens, an optic, an optic surface, orat least a portion of an optic surface to redirect incident light forthe purpose of forming a real or virtual focus or focal point. Theoptical power may result from reflection, refraction, diffraction, orsome combination thereof and is generally expressed in units ofDiopters. One of skill in the art will appreciate that the optical powerof a surface, lens, or optic is generally equal to the reciprocal of thefocal length of the surface, lens, or optic when the focal length isexpressed in units of meters. As used herein, the term “refractiveoptical power” or “refractive power” means optical power produced by therefraction of light as it interacts with a surface, lens, or optic. Asused herein, the term “diffractive optical power” or “diffractive power”means optical power resulting from the diffraction of light as itinteracts with a surface, lens, or optic, for example as produced by adiffraction order of a phase plate. When used in reference to a phaseplate, the term “diffractive optical power” or “diffractive power” meansthe substantially equivalent optical power attributed to a refractivelens that converges or diverges light at a design wavelength insubstantially the same manner as the diffractive phase plate for whichthe term is used.

FIG. 1 illustrates a prior art bifocal IOL 20 with an optical axis 21disposed in an eye 22. The IOL 20 comprises phase plate 23 made, forexample, in accordance with the teachings of Freeman in U.S. Pat. No.4,642,112 or Cohen in U.S. Pat. No. 5,144,483. The phase plate 23 isdisposed on an anterior surface 24 having a base curvature C and isilluminated by incident light 26 from a distant object that enters theeye 22 in the form of collimated light. A first portion 27 of theincident light 26 is substantially unaffected by the phase plate 23 andis focused by the anterior surface 24 and a posterior surface 28 throughrefraction to produce a first focus 29 approximately located on a retina30 of the eye 22 for providing distant vision. A second portion 32 ofthe incident light 26 is diffracted by the phase plate 23 to form asecond focus 34 for providing near or intermediate vision. The netoptical power of the anterior surface 24 for forming the second focus 34is generally considered to be a combination of (1) a refractive opticalpower of the anterior surface 24 due to the base curvature C and (2) adiffractive optical power of the phase plate 23. It will be appreciatedthat in an actual eye, the light forming the second focus 34 wouldcontinue propagating towards the retina 30; however, this light isillustrated as terminating at the second focus 34 for purposes ofclarity.

The term “near vision,” as used herein, refers to vision provided by atleast a portion of a lens, such as the IOL 20, or an imaging system,wherein objects relatively close to the subject are substantially infocus on the retina of the eye of a subject. The term “near vision”generally corresponds to vision provided when objects are at a distancebetween about 25 cm to about 50 cm. Conversely, the term “distantvision,” as used herein, refers to vision provided by at least a portionof a lens or imaging system, wherein objects relatively far from thesubject are substantially on the retina of the eye. The term “distantvision” generally corresponds to vision provided when objects are at adistance of at least about 1 meter to about 2 meters away from thesubject, preferably at a distance of 5 to 6 meters or greater. The term“intermediate vision” generally refers to vision provided by at least aportion of a lens or imaging system, wherein objects at an intermediatedistance from the subject are substantially in focus on the retina ofthe eye. Intermediate vision generally corresponds to vision providedwhen objects are at a distance of about 40 centimeters to about 1.5meters.

Referring again to FIG. 1, the IOL 20 effectively has two optical powersdue to the combination of the anterior surface 24, the posterior surface28, and the phase plate 23. It will be appreciated that the IOL 20 mayhave additional optical powers since the incident light 26 wouldnormally be diffracted into other higher and lower diffraction orders.For instance, when the phase plate 23 is made according to the teachingsof Cohen in the '483 patent, approximately 80% of the light at a designwavelength is approximately evenly split between a zeroth diffractionorder and a first diffraction order, while the remaining 20% of thelight is split between higher diffraction orders (e.g., greater than a+1 diffraction order) and/or lower diffraction orders (e.g., less thanor equal to a −1 diffraction order) of the phase plate 23.

FIG. 2 illustrates the performance of the IOL 20 for a near object 40located relatively close to the eye 22. Under these conditions, thedistant and near foci 29, 34 are disposed such that the near focus 34 isapproximately located on the retina 30 and the distant focus 29 islocated behind the retina 30. Therefore, the IOL 20 may function as abifocal lens that provides a patient with both near vision and distantin a way that at least approximates the accommodative ability of thenatural lens lost due to presbyopia and/or removal of the natural lens.

The phase plate 23 of the bifocal IOL 20 generally comprises a pluralityof annular zones, facets, or echelettes having a particular offset orstep height between adjacent zones along the optical axis 21. As usedherein, the terms “zone”, “facet”, or “echelette” are usedinterchangeably to mean portions of a zone or phase plate disposedbetween steps or other phase discontinuity thereon.

The bifocal characteristics of the IOL 20 may be realized by selectingthe step height between adjacent zones to be such that rays to eitherside of the step experience a difference in optical path length of λ/2,where λ is a design wavelength. For instance, if the bifocal IOL 20 ismade of material having a refractive index of n_(IOL) and the materialadjacent to the anterior surface 24 is n₀, then the step height h_(step)is given by the relationship:

$\begin{matrix}{{h_{step} = \frac{\lambda}{2\left( {n_{IOL} - n_{o}} \right)}},} & (1)\end{matrix}$herein referred to as a λ/2 phase plate. The height of the step may alsobe referred to herein by its phase height. For example, the step heighth_(step) given by Equation (1) will be referred to as a λ/2 phase stepheight. As will be appreciated by those of skill in the art, a λ/2 phaseplate may be used to produce zeroth and first diffraction ordercontaining approximately 40% each of the total light diffracted by thephase plate. This type of phase plate may be referred to as a MOD 0.5phase plate, indicating that the step height corresponds to an opticalpath length difference of 0.5 times the design wavelength λ.

Alternatively, the IOL 20 may be in the form of a monofocal IOL in whichthe step height is such that rays to either side of the step betweenadjacent zones experience a difference in optical path length of λ. Sucha phase plate will be herein referred to as a 1λ phase plate and ashaving a 1λ phase step height. Thus, for the material refractive indicesjust used, a step height given by the relationship:

$\begin{matrix}{{h_{step} = \frac{\lambda}{\left( {n_{IOL} - n_{o}} \right)}},} & (2)\end{matrix}$provides a monofocal IOL in which essentially 100% of the energy in theincident light 26 is diffracted into the first diffraction order of thephase plate 23 and, therefore, into the near focus 34. This type ofphase plate may be referred to as a MOD 1 phase plate, indicating thatthe step height corresponds to an optical path length difference of onetimes the design wavelength λ.

The phase plate 23 may alternatively be constructed so that the stepheight between adjacent zones is such that rays to either side of thestep experience a difference in optical path length of 3λ/2, as taughtby Futhey in U.S. Pat. No. 5,229,797. In this case the location of thedistant and near foci 29, 34 are provided by the combination of therefractive powers of the anterior and posterior surfaces 24, 28 and thefirst and second diffraction orders of the phase plate 23. This type ofphase plate may be referred to as a MOD 1.5 phase plate, indicating thatthe step height corresponds to an optical path length difference of 1.5times the design wavelength λ. Higher MOD phase plates are taught byFaklis et al. in U.S. Pat. No. 5,589,982, which is herein incorporatedby reference.

Based on this convention, a MOD x.5 phase plate, where x is an integer,is a phase plate with a step height between adjacent zones correspondingto an optical path length difference of (x+½) times the designwavelength λ, where x is an integer greater than or equal to one. MODx.5 phase plates are characterized in that most of the energy from lightincident on the phase plate is generally split between two diffractionorders. A MOD x phase plate refers to one in which the step heightbetween adjacent zones corresponds to an optical path length differenceof x times the design wavelength λ, where x is an integer greater thanor equal to one. MOD x phase plates are characterized in that most orall of the energy from incident light is contained in a singlediffraction order. This same convention can also be applied to phaseplates having no physical step height between adjacent zones. Forexample, the phase plate 23 could be produced using holographic or othersuch methods to form of a MOD x phase plate in which phase changebetween adjacent zones is the same as that produced by a substantiallyequivalent phase plate having a step height between adjacent zonescorresponding to an optical path length difference of x times the designwavelength λ. Alternatively, the various zones may be provided in theform of a transmission grating.

Referring to FIG. 3, in certain embodiments of the present invention, anophthalmic lens 100 comprises an optic 102. The optic 102 has ananterior surface 104, a posterior surface 106, and an optical axis 108.The optic 102 comprises a first region 110 having an optical power andcomprising a multifocal phase plate 112 for providing, producing, orforming a first focus or focal point F1 and a second focus or focalpoint F2 The optic 102 further comprises a second region 120 having anoptical power and comprising a monofocal phase plate 122 for providing,producing, or forming a third focus F3. As a general convention, lightrays produced by the interaction of light from an object with a bifocalor multifocal phase plate, such as the multifocal phase plate 112, arerepresented in the figures by lighter weight lines than those light raysproduced by the interaction of light from an object with a monofocalphase plate, such as the monofocal phase plate 122. For example, aninput light ray 124 illustrated in FIG. 3 is split into two focusedlight rays 124 a and 124 b directed to the first focus F1 and the secondfocus F2, respectively, which are represented by lighter weight lines.By contrast, an input light ray 126 illustrated in FIG. 3 produces asingle focused light ray 126 a that is directed to the third focus F3,which is represented by heavier weight line.

The ophthalmic lens 100 may be an intraocular lens for placement ineither the posterior or anterior chambers of a mammalian eye. As such,the ophthalmic lens 100 may be used to replace the natural lens of theeye, for example after removal of the natural lens during cataractsurgery. Alternatively, the ophthalmic lens 100 may be a phakic lensthat is disposed either in front of the iris, behind the iris, or in theplane defined by the iris. Alternatively, the ophthalmic lens 100 may bea corneal implant that is, for example, inserted within the stromallayer of the cornea. The ophthalmic lens 100 may also be a contact lensor some other type of ophthalmic device that is used to provide orimprove the vision of a subject. The ophthalmic lens 100 may also beused as part of an imaging system, for example to supplement or correcta previously implanted IOL or corneal implant, or in an accommodatinglens system similar to that disclosed by Lang et al. in U.S. Pat. No.6,231,603, herein incorporated by reference.

The ophthalmic lens 100 may be constructed of any of the commonlyemployed material or materials used for rigid optics, such aspolymethylmethacrylate (PMMA), or of any of the commonly used materialsfor resiliently deformable or foldable optics, such as siliconepolymeric materials, acrylic polymeric materials, hydrogel-formingpolymeric materials, such as polyhydroxyethylmethacrylate,polyphosphazenes, polyurethanes, and mixtures thereof and the like. Thematerial preferably forms an optically clear optic and exhibitsbiocompatibility in the environment of the eye. The ophthalmic lens 100may be made of or contain materials useful for forming the phase plates112, 122 such as photosensitive materials (e.g., photopolymer or silverhalide) or a variable refractive index material. Portions of the optic102 may be constructed of a more opaque material, for example toselectively block light at the boundaries between the phase plates 112,122 or between adjacent zones of within the phase plates 112, 122. Suchmaterial might serve to reduce scattered light or to otherwise define ormodify the performance of either or both of the phase plates 112, 122.

The selection of suitable lens materials is well known to those of skillin the art. See, for example, David J. Apple, et al., IntraocularLenses: Evolution, Design, Complications, and Pathology, (1989) William& Wilkins. Foldable/deformable materials are particularly advantageoussince optics made from such deformable materials may be rolled, foldedor otherwise deformed and inserted into the eye through a smallincision. The lens material preferably has a refractive index allowing arelatively thin, and preferably flexible optic section, for example,having a thickness in the range of about 150 microns to about 1000microns, and preferably about 150 microns or about 200 microns to about500 microns. When the ophthalmic lens 100 is an intraocular lens, theoptic 102 may have a diameter of about 4 mm or less to about 7 mm ormore, preferably about 5.0 mm to about 6.0 mm or about 6.5 mm.

When configured as an IOL, the ophthalmic lens 100 may comprise any ofthe various means available in the art for centering or otherwisedisposing the optic 102 within the eye. For example, ophthalmic lens 100may comprise one or more fixation members or haptics. The haptics may bemade of the same material as the optic 102 and/or integrally formedtherewith to form a one-piece IOL. Alternatively, one or more hapticsmay be formed separately and attached to the optic 102 to provide amulti-piece configuration. The fixation members may comprise any of avariety of materials which exhibit sufficient supporting strength andresilience, and/or which are substantially biologically inert in theintended in vivo or in-the-eye environment. Suitable materials for thispurpose include, for example, polymeric materials such as siliconepolymeric materials, acrylic polymeric materials, hydrogel-formingpolymeric materials, such as polyhydroxyethylmethacrylate,polyphosphazenes, polyurethanes, and mixtures thereof and the like. Inother embodiments, the ophthalmic lens 100 comprises a positioning meansthat allows the optic 102 to move along the optical axis 108 in responseto deformation of the capsular bag and/or in response to the ciliarymuscles of the eye.

In certain embodiments, the monofocal phase plate 122 and the multifocalphase plate 112 are both disposed on the anterior surface 104, as shownin FIG. 3. Alternatively, the monofocal phase plate 122 and themultifocal phase plate 112 are both disposed on the posterior surface106. In other embodiments, the monofocal phase plate 122 and themultifocal phase plate 112 are be disposed on opposite surfaces 104, 106of the optic 102. For example, the multifocal phase plate 112 may bedisposed on the anterior surface 104, while the monofocal phase plate122 is disposed on the posterior surface 106.

The first region 110 with the multifocal phase plate 112 may be disposedin the center of the optic 102 and the second region 120 with themonofocal phase plate 122 may be disposed outside the first region 110.Alternatively, the second region 120 may be disposed in the center ofthe optic 102 and the first region 110 may be disposed outside thesecond region 120. The phase plates 112, 122 preferably each have acircular outer diameter when viewed from the front.

The multifocal phase plate 112 may comprise a first plurality 128 ofdiffraction zones, facets, or echelettes 130, while the monofocal phaseplate 122 comprises a second plurality 132 of diffraction zones 130. Thefirst region 110 typically includes a central diffraction zone 134 thatis substantially circular and is surrounded by the remaining diffractivezones 130 that typically have an annular shape. Determination of theouter diameter of each of the diffraction zones 130 is well known in theart and is generally a function of a design wavelength λ, and thedesired focal length of the lens. The design wavelength λ may beanywhere within the electromagnetic spectrum, for example in visible,infrared or ultraviolet wave bands. The design wavelength λ is generallyin the visible waveband and is preferably in the range of approximately400 nm to approximately 800 nm, more preferably in the range ofapproximately 500 nm to approximately 600 nm, even more preferably inthe range of 540 nm to 560 nm. In some embodiments, the designwavelength λ is approximately 500 nm, approximately 546 nm, orapproximately 550 nm.

When the multifocal phase plate 112 is disposed in the center of theoptic 102, as illustrated in FIG. 3, the multifocal phase plate 112 hasan outer diameter D. Each of the diffraction zones 130 preferably havean area that is substantially the same as each of the remainingdiffractive zones 130; however, the central zone 134 may optionally havean area that is either less than or greater than the area of theremaining annular diffractive zones 130 as taught, for example, by theFuthey '718 patent or the Cohen '980 patent.

When the ophthalmic lens 100 is an IOL, the diameter D may be selectedsuch that the iris of the eye substantially prevents light from passingthrough the monofocal phase plate 122 under bright lighting conditions.The outer diameter D is preferably less than approximately 5 mm, morepreferably less than less than about 4 mm. In certain embodiments, thedesign wavelength λ is approximately 550 nm and the outer diameter D isapproximately 3.0 mm in diameter and comprises 8 diffraction zones 130,including the central diffraction zone 134. In other embodiments, theouter diameter D is approximately 3.3 mm, 3.6 mm, or 3.9 mm andcomprises 10, 12, or 14 diffraction zones 130, respectively.

The diffractive zones 130 are preferably offset parallel to the opticalaxis 108 so as to form steps 138 between adjacent zones 130, the steps138 being selected to produce a predefined phase relationship betweeneach of the diffractive zones 130. The size of the steps 138 betweenadjacent zones 130 in the multifocal phase plate 112 are preferablydifferent from the size of the steps 138 between adjacent zones 130 inthe monofocal phase plate 122. In certain embodiments, the diffractivezones 130 are formed by refractive index variations within the firstregion 110, the second region 120, or both so as to provide apredetermined phase relationship between the various zones 130 of themultifocal and/or monofocal phase plates 112, 122. The use of materialand methods discussed above herein may be used to form the diffractivezones 130 so as to eliminate, or at least reduce the size of, the steps138 between adjacent zones 130. Preferably, the variation in refractiveindex across the surfaces is in a radial direction from the center ofthe optic. A predetermined refractive index variation may be producedwhen either the multifocal phase plate 112 or the monofocal phase plate122 is a phase hologram. Such holograms may be produced using a materialsuch as photopolymer or silver halide, in which the refractive index maybe varied by exposure to a holographically formed interference pattern.Other means for producing the phase plates 112, 122 are also anticipatedand consistent with embodiments of the ophthalmic lens 100. The hologramcould alternatively take the form of a transmission hologram in whichthe transmission varies with distance from the optical axis.

The multifocal phase plate 112 and monofocal phase plate 122 may bedisposed on or about a base curvature C1 such that the regions 110, 120have a refractive optical power that is separate from a diffractiveoptical power produced by the phase plates 112, 122. As illustrated inFIG. 3, the refractive optical power of regions 110, 120 may be producedby forming the ophthalmic lens 100 as a biconvex lens; however, otherlens forms may be used such as, for example, a plano-convex,plano-concave, concave-concave, or meniscus lens. In addition, theoptical power of the ophthalmic lens 100 may be either positive ornegative. For example, when the ophthalmic lens 100 is an IOL for apseudophakic eye, the IOL will generally have a positive optical power;however, when the ophthalmic lens 100 is used as a phakic IOL (e.g., oneused in an eye containing the natural lens), the IOL can have either apositive or negative optical power, depending on the ocular conditionbeing corrected.

The overall profile or shape of the anterior surface 104 and theposterior surface 106 may be any that is commonly used for producing anoptic based on refraction of incident light. For instance, the overallshape or profile of the anterior surface 104, as represented by the basecurvature C1, may be spherical with an overall radius of curvature R1(not shown) that is generally finite (i.e., is not flat or substantiallyflat, that is with surface deviations on the order of about a wavelengthof visible light or less). The detailed profile of the anterior surface104 in the area of the first region 110 is the summation of the basecurvature C1 and the profile of the multifocal phase plate 112.Similarly, the detailed profile of the anterior surface 104 in the areaof the second region 120 is the summation of the base curvature C1 andthe profile of the monofocal phase plate 122.

Alternatively, the overall profile or shape of either the anteriorsurface 104, the posterior surface 106, or both the surfaces 104, 106may be parabolic, elliptical, hyperbolic, or any aspheric shape commonin the art, for example, for reducing aberrations such as sphericalaberrations or astigmatism. For example, the posterior surface 106 maybe an aspheric surface designed to reduce spherical aberrations based oneither an individual cornea or group of corneas as described by Piers etal. in U.S. Pat. Nos. 6,609,673 and 6,830,332 and U.S. patentapplication Ser. No. 10/724,852, all herein incorporated by reference.Other aspheric and asymmetric surface profiles of the anterior surface104 and the posterior surface 106 of use within the art are alsoconsistent with embodiments of the ophthalmic lens 100. For example, theposterior surface 106, or both the surfaces 104, 106 may be defined ashaving a central lens radius of R1 and a conic constant of k. In suchembodiments, the surface profile z may, in a non-limiting example, bedefined by the equation:

$\begin{matrix}{{z = {\frac{\left( \frac{1}{R\; 1} \right)r^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)\left( \frac{1}{R\; 1} \right)^{2}r^{2}}}} + {a_{4}r^{4}} + {a_{6}r^{6}} + \ldots}}\mspace{14mu},} & (3)\end{matrix}$where r is the radial distance from the optical axis and z the sag inthe direction of light propagation, and a₄, a₆ . . . are coefficients.

The refractive optical power of the first and second regions 110, 120are preferably within a range of about −10 Diopters to at least about+50 Diopters, more preferably within a range of at least about +10Diopters to at least about +40 Diopters, and most preferably within arange of at least about +10 Diopters to at least about +30 Diopters. Themost preferred range is typical of IOLs used in aphakic eyes, forinstance after cataract surgery. When the ophthalmic lens 100 is aphakic IOL (an IOL used in an eye still having the natural lens), therefractive optical power of the first and second regions 110, 120 arepreferably within a range of at least about −30 Diopters to at leastabout +30 Diopters, more preferably within a range of at least about −20Diopters to at least about +20 Diopters, and even more preferably withina range of at least about −10 Diopters to at least about +10 Diopters.Other ranges of the refractive optical power may be preferred, dependingon the particular application and type of ophthalmic lens to be used.

Preferably, the refractive optical power of the first and second regions110, 120 are much greater than the diffractive optical powers of themultifocal phase plate 112 and/or the monofocal phase plate 122. Forexample, if the ophthalmic lens 100 is an IOL for a pseudophakic eye,the refractive optical power of the first and second regions 110, 120 ispreferably at least about 10 Diopters to at least about 40 Diopters,while the multifocal and monofocal phase plates 112, 122 have at leastone diffraction order, for instance a first diffraction order, with adiffractive optical power of at least about +2 Diopters to at leastabout +6 Diopters, preferably about +4 Diopters.

The total optical power of the second region 120 may be regarded as thesummation of the refractive optical power of the second region 120 andthe diffractive optical power of the monofocal phase plate 122. Forinstance, if the refractive optical power is 30 Diopters and thediffractive optical power is +4 Diopters, the total optical power of thesecond region 120 would be approximately 34 Diopters. Because themultifocal phase plate 112 produces at least two diffraction orders, thefirst region 110 may be considered as having at least two effectiveoptical powers. For instance, the first region 110 may be configured tohave a refractive optical power of 30 Diopters and a multifocal phaseplate 112 that produces a zeroth diffraction order having no opticalpower and a first diffraction order having a diffractive optical powerof +4 Diopters. Using this configuration, the multifocal phase plate 112may be considered as having a first effective optical power that isapproximately equal to the refractive optical power of 30 Diopters and asecond effective optical power of 34 Diopters, that is, the summation ofthe refractive optical power (30 Diopters) and the diffractive opticalpower of the first diffraction order of multifocal phase plate 112 (+4Diopters). The additional optical power of +4 Diopters provided by themultifocal phase plate 112 is referred to herein as the “add power” ofthe multifocal phase plate 112.

There are at least two potential benefits of an ophthalmic lens 100 asdescribed in the previous paragraph. First, the add power produced bythe first diffraction order of the multifocal phase plate 112 is suchthat the location of the first focus F1 and the second focus F2 alongthe optical axis 108 may be configured to provide both near vision anddistant vision. That is, the first focus F1 is configured to providedistant vision, while the add power of the multifocal phase plate 112 isconfigured such that the second focus F2 provides near vision.Alternatively, the add power may be such that the first focus F1provides distant vision, while the second focus F2 provides intermediatevision, for instance where the ophthalmic lens 100 is part of anaccommodation lens system in which some accommodation is provided by amovement assembly that is responsive to the capsular bag and/or theciliary muscles of the eye.

A second potential benefit of the above configuration is related to thechromatic dispersion produced by the first diffraction order of themultifocal and monofocal phase plates 112, 122. It is known in the artthat chromatic dispersion of a first diffraction order is usuallyopposite in sign from the chromatic dispersion of typical refractivematerials. The amount of negative dispersion resulting when thediffractive optical power is in the range of about +2 Diopters to about+4 Diopters is also approximately the amount of dispersion needed tooffset the positive dispersion present in many optical materials, suchas silicone or acrylic. Thus, the combination of a refractive lens withan optical power of about 20 to 40 Diopters with, for example, amultifocal phase plate having an add power of about +2 to +4 Dioptersproduces an optical element with reduced overall chromatic aberrations,since the refractive chromatic dispersion and diffractive chromaticdispersion approximately cancel one another.

Alternatively, the diffractive optical power of the phase plates 112,122 may be outside the above range of about +2 Diopters to about +4Diopters. The selected value of the diffractive optical power can dependon such parameters as the refractive optical power of the phase plates112, 122, the total optical power of the ophthalmic lens 100, and thedesired interaction between the diffractive and refractive components ofthe ophthalmic lens 100. The diffractive optical power of one or both ofthe phase plates 112, 122 may also be a negative Diopter power. Thephase plates 112, 122 may otherwise be configured to adjust thechromatic aberrations of one or more of the first focus F1, the secondfocus F2, and the third focus F3. Also, the phase plates 112, 122 may beconfigured to adjust other monochromatic aberrations of one or more ofthe first focus F1, the second focus F2, and the third focus F3 (e.g.,spherical aberrations, astigmatism, etc.).

In certain embodiments, the multifocal phase plate 112 may be a bifocalphase plate in which light incident upon the multifocal phase plate 112is split primarily between two different diffraction orders, for examplebetween the zeroth and first diffraction orders or between the first andsecond diffraction orders. The first region 110 and the multifocal phaseplate 112 may be disposed such that light in the two diffraction ordersare used to provide, for example, distant and near vision or distant andintermediate vision. In such embodiments, some light is usually alsocontained in other diffraction orders. The multifocal phase plate 112may be configured to provide a significant amount of light in three ormore diffraction orders. For example the multifocal phase plate 112could provide three diffraction orders to provide near, intermediate,and distant vision or to provide an effectively increased depth offield.

In the illustrated embodiment shown in FIG. 3, the multifocal phaseplate 112 is a MOD 1.5 phase plate and the monofocal phase plate 122 isa MOD 1 phase plate; however, other combinations of MOD x.5 and/or MOD yphase plates for the phase plates 112, 122 are consistent withembodiments of the present invention. The multifocal and monofocal phaseplates 112, 122 may be configured such that the first focus F1 and thirdfocus F3 are disposed at the same or substantially the same location. Asused herein the term “substantially the same location,” when used inreference to two or more foci of an optic or IOL according toembodiments of the invention, means (1) that the locations of the fociformed by light from two portions of an optic or IOL according toembodiments of the invention differ by no more that the depth of fieldor depth of focus of the portions, either individually or takentogether, or (2) that the locations of the foci formed by light from twoportions of an optic or IOL according to embodiments of the inventiondiffer by an amount that is too small to be clinically significant(e.g., that difference in the locations of the two foci formed by thetwo portions of the optic or IOL is so small that an average patientwould not detect a difference in the vision between a traditional IOLhaving a focal length equal to that of the first portion and atraditional IOL having a focal length equal to that of the secondportion).

The multifocal phase plate 112 may be configured to produce a firstdiffraction order and a second diffraction order that each containapproximately 40% of the incident energy on the optic. The multifocalphase plate 112 and the base curvature C1 may be selected such that thefirst diffraction order corresponds to the first focus F1 and providesdistant vision, while the second diffraction order corresponds to thesecond focus F2 and provides either near or intermediate vision. Inaddition, the MOD 1 phase plate 122, which provides primarily a firstdiffraction order only, may be configured to also provide distantvision.

The outer diameter D of the multifocal phase plate 112 may be selectedto be approximately the same dimension as the pupil of the eye whenunder moderate to bright lighting conditions, such that little or nolight is received by the second region 120 and the monofocal phase plate122. Thus, most of the light received by the eye is received by thefirst region 110 and the multifocal phase plate 112, which provides bothnear vision and distant vision in approximately equal proportions. Underlower light conditions, such a normal room light or dim lighting, theiris of the eye normally dilates to a larger diameter so that more lightenters the second region 120 and the MOD 1 phase plate 122. Thus, underlower lighting conditions, more light is directed to distant vision asthe iris dilates, since all the light entering the monofocal phase plate122 goes to providing distant vision. Therefore, the ophthalmic lens 100favorably provides better distant vision under lower lighting conditionsby directing a higher percentage of the available light to the distantvision. Such a lens is sometimes referred to as a “distant dominantlens.”

In other embodiments, as illustrated in FIG. 4 for instance, themultifocal phase plate 112 is a MOD 1.5 phase plate and the monofocalphase plate 122 is a MOD 2 phase plate. In such embodiments, the firstfocus F1 provides distant vision and the second focus F2 provides nearor intermediate vision, while the monofocal phase plate 122 produces thethird focus F3, which may provide either near or intermediate vision.Thus, the ophthalmic lens 100 is configured such that the second focusF2 and third focus F3 are disposed at substantially the same location.

If the outer diameter D of the multifocal phase plate 112 is againselected to be approximately the same dimension as the pupil of the eyeunder bright lighting conditions, little or no light is received by thesecond region 120 and the monofocal phase plate 122 under such lightingconditions. However, in this configuration, as the iris of the eyedilates to a larger diameter, more light is directed to near orintermediate vision as the iris dilates, since all the light enteringthe MOD 2, monofocal phase plate 122 goes to providing near orintermediate vision. In this embodiment, therefore, the ophthalmic lens100 provides better near or intermediate vision under lower lightingconditions and is referred to as a “near dominant lens.”

Referring to FIG. 5, in some embodiments, the multifocal phase plate 112of the ophthalmic lens 100 is a MOD 0.5 phase plate and the monofocalphase plate 122 is a MOD 1 phase plate. In such embodiments, the phaseplates 112, 122 may both be disposed on the single base curvature C1.The MOD 0.5 phase plate 112 usually produces a zeroth diffraction orderand first diffraction order which may be configured to correspond todistance vision and near or intermediate vision, respectively. The MOD 1phase plate 122 also provides near or intermediate vision and has asingle, first diffraction order which corresponds to the second focusF2. Thus, the second focus F2 produced by the MOD 0.5 phase plate 112and third focus F3 produced by the MOD 1 phase plate are disposed atsubstantially the same location.

Preferably, the zeroth and first diffraction orders of the MOD 0.5 phaseplate 112 are configured so that each diffraction order containsapproximately 40% of the incident energy received by the optic 102,although other percentages for the two diffraction orders are alsopossible. Preferably, the ophthalmic lens 100 is configured to favorablyprovide a reduction in chromatic aberrations for near or intermediatevision, by selecting the phase plates 112, 122 so that the firstdiffraction orders of both phase plates 112, 122 produce negativedispersion that balances the positive dispersion produced by therefractive power of the first and second regions 110, 120.

As illustrated in FIG. 5, the ophthalmic lens 100 is a near dominantlens, since more of the MOD 1 phase plate 122 is exposed as the pupil ofthe eye in which the ophthalmic lens 100 is used dilates under lowerlighting conditions. In certain instances, however, it may be preferredthat the ophthalmic lens 100 be a distant dominant lens. One way ofaccomplishing this objective is to eliminate the monofocal phase plate122 altogether, so that the second region 120 has only a refractiveoptical power, as discussed in greater detail below herein. Onepotential problem with this approach is the loss of the favorablechromatic aberration reduction provided by the negative dispersion ofthe monofocal phase plate 122.

An innovative way has been developed for overcoming this potentialproblem in which the ophthalmic lens 100 is simultaneously a distantdominant lens and able to provide reduced chromatic aberrations.Referring to FIG. 6, in certain embodiments, the ophthalmic lens 100comprises the optic 102, the first region 110, and the second region120, wherein the first region 110 comprises a multifocal phase plate 112disposed on a first base curvature C1 that may have a first radius ofcurvature R1 (not shown) and the second region 120 comprises a monofocalphase plate disposed on a second base curvature C2 that may have asecond radius of curvature R2 (not shown), the radius of curvatures R1,R2 being generally finite (i.e., are not flat or substantially flat,that is with surface deviations on the order of a wavelength of light orless). In such embodiments, the first radius of curvature R1 isdifferent from the second radius of curvature R2. The first region 110and second region 120 each have a refractive optical power that isproduced by the finite radius of curvatures R1, R2, respectively.

The multifocal phase plate 112 may be configured to provide, produce, orform the first focus or focal point F1 and the second focus or focalpoint F2, where the location of the foci F1, F2 may be affected by therefractive optical power of the regions 110. For example, the secondbase curvature C2 may be configured such that the first focus F1 andthird focus F3 are disposed at substantially the same location so as toprovide distant vision, rather than near or intermediate vision, as inembodiments of the ophthalmic lens 100 illustrated in FIG. 5. Oneunexpected result of the present embodiment is that at least somereduction in chromatic aberrations may be provided both for distantvision and for near or intermediate vision, since the first diffractionorder of the MOD 0.5 phase plate 112 reduces chromatic aberrations fornear or intermediate vision, while the first diffraction order of theMOD 1 phase plate 122 is now configured to reduce chromatic aberrationsfor distant vision.

In certain embodiments, the base curvatures C1, C2 are spherical orsubstantially spherical in shape, while in other embodiments, one ormore of the base curvatures C1, C2 may be aspheric and/or asymmetric inshape (e.g., have a surface shape that is other than a spherical shape).As used herein, the term “substantially spherical” means that deviationsin the shape of a surface from that of a spherical surface are less thanat least about 10 wavelengths of visible light, preferably less than 5wavelengths of visible light, and even more preferably less than 1wavelengths of visible light. It will be understood by those of skill inthe art that an aspheric surface is generally characterized by a radiusof curvature (e.g. the R1, R2), wherein the shape of at least a portionof the aspheric surface deviates from that of a sphere having thecharacteristic radius of curvature. In such embodiments, the asphericbase curvature may be characterized by the radii R1, R2, respectively.For example, one or both of the base curvatures may be defined by anaspheric equation such as Equation (3) in which R1 and/or R2 represent acentral lens radius of the corresponding base curvature.

In certain other embodiments, as illustrated in FIG. 7, the MOD 1 phaseplate 122 and radius of curvature R2 of the second base curvature C2 maybe configured independently of the first region 110 parameters such thatthe third focus F3 produced by the second region 120 is located onneither the first focus F1 nor the second focus F2 produced by the firstregion 110. For example, the second base curvature C2 may be configuredsuch that the third focus F3 is disposed along the optical axis betweenthe first focus F1 and the second focus F2. In such embodiments, thefirst focus F1 may provide distant vision, while the second focus F2 mayprovide near vision and the third focus F3 may provide intermediatevision. Alternatively, the MOD 1 phase plate 122 and the second basecurvature C2 could be configured to locate the third focus F3 at anypreferred location either on optical axis 108 or some distance off theoptical axis 108, for instance, to accommodate macular degeneration. Ingeneral, the parameters defining the phase plate 122 and the second basecurvature C2 may be selected to provide a focus that is completelyindependent of the first and second foci F1, F2 in terms of location,chromatic aberrations, or other focus parameters or characteristics. Forexample, the second region 120 of the ophthalmic lens 100 may beconfigured so that most of the light diffracted by the phase plate 122is contained in a −1 diffraction order, which provides, among otherthings, a positive amount of chromatic dispersion.

In still other embodiments, the multifocal phase plate 112 is a MOD x.5phase plate and monofocal phase plate 122 is a MOD y phase plate, wherex and y are integers, as explained above herein. For example, x may begreater than or equal to 2 such that the x^(th) diffraction ordercorresponds to the first focus F1 and provides distant vision, and the(x+1)^(th) diffraction order corresponds to the second focus F2 andprovides near or intermediate vision. The monofocal phase plate 122 maybe configured so that most of the diffractive optical power correspondsto either the first focus F1 (e.g., y=x) or second focus F2 (e.g.,y=x+1), depending on whether the ophthalmic lens 100 is to be distantdominant lens or near dominant lens, respectively. Alternatively, theophthalmic lens 100 may be configured so that most of the lightdiffracted by at least one of the phase plates 112, 122 is contained ina −1 diffraction order.

In addition to the various parameters and preferred ranged outlinedabove herein, embodiments of the ophthalmic lens 100 advantageouslyprovide a lens designer with additional independent parameters, such asthe independent choice of the radius of curvatures R1, R2 of the firstand second base curvatures C1, C2, respectively. In some embodiments,the step height between the diffraction zones 130 of the one of thephase plates 112, 122 is selected based on a design wavelength that isdifferent from the design wavelength selected for the other phase plate112, 122. For example, the step height between diffractive zones orechelettes 130 for the monofocal phase plate 122 may be selected basedon a design wavelength that is shifted toward a bluer wavelength ascompared to the design wavelength for the multifocal phase plate 112.The selection of a blue shifted design wavelength for the monofocalphase plate 122 may for example, advantageously provide better scotopicvision due to the eyes greater sensitivity to light in blue wavelengthband. In general, a design parameter or configuration discussed withregard to one embodiment of the ophthalmic lens 100 illustrated in oneof the figures is also available for embodiments of the ophthalmic lens100 illustrated in the other figures.

Referring to FIG. 8, the ophthalmic lens 100 may further comprise athird region 140 having a refractive optical power, where the thirdregion 140 comprises a third phase plate 142. The third phase plate 142may, for example be a multifocal phase plate or a monofocal phase plate.In such embodiments, the third region 140 may be disposed between thefirst region 110 and the second region 120, as illustrated in FIG. 8.Alternatively, the third region 140 may be disposed outside the firstregion 110 and the second region 120. The third region 140 may furthercomprise a third base curvature C3 having a radius of curvature R3,where the third base curvature C3 is either different from the basecurvatures C1, C2 of the first and second regions 110, 120 or,alternatively, be substantially the same as at least one of the basecurvatures C1, C2 (e.g., having the same radius of curvature as the basecurvature C1). In certain embodiments, the base curvatures C1, C2, C3are spherical or substantially spherical in shape, while in otherembodiments, one or more of the base curvatures C1, C2, or C3 may beaspheric and/or asymmetric in shape.

In certain embodiments, the third region 140 may be an intermediateregion disposed between the first region 110 and the second region 120so that the third phase plate 142 is disposed between the multifocal andmonofocal phase plates 112, 122. In such embodiments, the intermediatephase plate 142 may be configured to provide a transition betweenmultifocal phase plate 112 and the monofocal phase plate 122. Forexample, the diffraction zones 130 of the intermediate phase plate 142may be configured to have steps 138 with a step size that is betweenthose of the multifocal and monofocal phase plates 112, 122. In oneembodiment, the step height between the diffraction zones 130 of theintermediate phase plate 142 are constant and is selected based on adesign wavelength that is different from the design wavelength selectedfor the multifocal phase plate 112 and the monofocal phase plate 122.Such a selection may be used advantageously to blur the edges of a haloformed by a bifocal or multifocal lens. In other embodiments, the stepheight between the diffraction zones 130 of the intermediate phase plate142 varies over the third region 140, for example, as a function ofradius.

For any of the embodiments of the ophthalmic lens 100 discussed herein,the multifocal phase plate 112 and the monofocal phase plate 122 may bedisposed in a manner that best suits a particular application or design.For instance, the monofocal phase plate 122 may be disposed in thecenter of the ophthalmic lens 100 and the multifocal phase plate 112outside the monofocal phase plate 122. Alternatively, both phase plates112, 122 may have annular shapes such that neither is disposed in thecenter of the ophthalmic lens 100. For example, the center of theophthalmic lens 100 may be a void, a refractive optical element, or someother type of optical element about which the phase plates 112, 122 aredisposed.

Referring to FIG. 9, in certain embodiments, the first region 110 of theophthalmic lens 100 comprises a first monofocal phase plate 144 disposedon the first base curvature C1 and the second region 120 of theophthalmic lens 100 comprises a second monofocal phase plate 145disposed on the second base curvature C2. The optical power of the firstbase curvature C1 may be greater than the optical power of the firstmonofocal phase plate 144 and the optical power of the second basecurvature C2 may be greater than the optical power of the secondmonofocal phase plate 145. Preferably, the first base curvature C1 has afinite first radius of curvature R1 that is different from a finitesecond radius of curvature m of the second base curvature C2. In thisway, the first radius of curvature R1 and the second radius of curvatureR2 are independent design parameters that may be advantageously selectedto be compatible with the first and second monofocal phase plates 144,145 in providing two or more foci.

The first monofocal phase plate 144 may be configured to produce achromatically corrected first focus FM1 providing distant vision and thesecond monofocal phase plate 145 may be configured to provide achromatically corrected second focus FM2 providing near or intermediatevision. This would advantageously provide a patient with both gooddistant vision under bright outdoor lighting conditions, where the pupilis relatively small, and better near or intermediate vision under dimmerindoor lighting conditions, where the pupil dilates to uncover more ofthe second monofocal phase plate 145.

It will be appreciated that the phase plates 144, 145 typically have ahigh amount of chromatic dispersion as compared to a refractive elementhaving a similar amount of optical power. As discussed above herein, thechromatic dispersion of the phase plates 144, 145 are also generallyopposite in sign to the chromatic dispersion of a refractive element. Asa result, the first and second monofocal phase plates 144, 145 may beadvantageously configured to have relatively low optical powers, suchthat their chromatic dispersion due to diffraction is approximately thesame magnitude, but opposite sign, as the chromatic dispersion of thefirst and second base curvatures C1, C2, which have relatively highoptical powers. Therefore, the resultant chromatic aberrations may besubstantially reduced for the combinations of the first monofocal phaseplate 144 with the first base curvature C1 and second monofocal phaseplate 145 with the second base curvature C2.

In other embodiments, the phase plates 144, 145 may both be multifocalphase plates or bifocal phase plates. In yet other embodiments, theophthalmic lens 100 may be configured so that most of the lightdiffracted by at least one of the phase plates 144, 145 is contained ina higher or lower diffraction order (e.g., a diffraction order otherthan the zeroth or first diffraction order). It will be appreciated thatthe various design parameters available for embodiments of theophthalmic lens 100 illustrated in any one of FIGS. 3-9 may, whenappropriate, also be available in the other embodiments of ophthalmiclens 100 discussed herein.

Referring to FIG. 10, in certain embodiments, an ophthalmic lens 200comprises an optic 202 having an anterior surface 204, a posteriorsurface 206, and an optical axis 208. The ophthalmic lens 200 furthercomprises a multifocal phase plate 212 configured to direct light to afirst focus F201 and a second focus F202, a monofocal phase plate 214configured to direct light to a third focus F203, and an intermediate ortransition phase plate 220 located between the multifocal phase plate212 and the monofocal phase plate 214. The multifocal phase plate 212comprises a first plurality 221 of echelettes 230 disposed on a firstbase curvature C201 having a first radius of curvature R201 andmonofocal phase plate 214 comprises a second plurality 222 of echelettes230 disposed on a second base curvature C202 having a second radius ofcurvature R202 that is preferably different from the first radius ofcurvature R201. The intermediate phase plate 220 comprises a thirdplurality 223 of echelettes 230 configured to change the overallresultant amplitude and/or distribution of light directed to the firstfocus F201 and/or the second focus F202. The third plurality 223 ofechelettes 230 are disposed on a third base curvature C203 having athird radius of curvature R203.

It will be appreciated that the various design parameters available forembodiments of the ophthalmic lens 100 illustrated in anyone of FIGS.3-9 may, when appropriate, also be incorporated into embodiments ofophthalmic lens 200. For example, in contrast to the embodimentsillustrated in FIG. 10, the multifocal phase plate 212 may be disposedat the periphery of the optic 202 and the monofocal phase plate 214 maybe disposed at or near the center of the optic 202. Additionally, thephase plates 212, 214 may alternatively be disposed on the posteriorsurface 206 rather than the anterior surface 204. In other embodiments,the phase plates 122 and the plates 212, 214 may be disposed on oppositesurfaces of the optic 202. In addition, any of the materials andgeometries discussed regarding the ophthalmic lens 100 may also beincorporated into the ophthalmic lens 200.

Referring again to the illustrated embodiment shown in FIG. 10, a set ofincident rays 232, for example from a distant point source, are incidenton the phase plates 212, 214, 220 of the ophthalmic lens 200. The use ofrays during the following discussion is illustrative only and is meantto point out certain inventive aspects of the ophthalmic lens 200. Theincident rays 232 interact with the ophthalmic lens 200 to producecorresponding focused rays 234. More specifically, the rays 232 incidenton the monofocal phase plate 214 produce focused rays 234 that aredirected to the third focus F203, as illustrated by the heavier weightlines in FIG. 10 representing the focused rays 234. The rays 232incident on the multifocal phase plate 212 and the intermediate phaseplate 220 produce focused rays 234 that are split between the first andsecond foci F201, F202, as illustrated by the lighter weight lines inFIG. 10 representing the focused rays 234. In the illustratedembodiment, first and third foci F201, F203 are disposed atsubstantially the same location. In certain embodiments, the first focusF201 and/or the third focus F203 may be disposed to provide distantvision and the second focus F202 may be disposed to provide near orintermediate vision. It will be appreciated by one of normal skill inthe art that the magnitude of the rays or the amount of light directedto the first and second foci F201, F202 by the phase plates 212, 220depends, at least in part, upon the step between adjacent echelettes 230of the phase plates 212, 220. The focused rays 234 focusing onto thesecond focus F202 continue to propagate to form an out-of-focus image onan image plane 238 passing through the first and/or third foci F201,F203. This out-of-focus image is referred to herein as “halo image”,consistent with the common usage of this term within the art. The imageplane 238 may be flat, as shown in FIG. 1, or have a more general shapesuch as a spheroid, for example, as in the case where the ophthalmiclens 200 is implanted into an eye as an IOL, wherein the image plane 238is the retina of the eye.

Referring to FIG. 11, the ophthalmic lens 200 shown in FIG. 10 isillustrated with a selected number of the incident rays 232 and focusedrays 234 in order to illustrate certain inventive aspects of theophthalmic lens 200. Specifically, an incident ray 240 incident justwithin the outer periphery of the monofocal phase plate 214 is directedto the third focus F203 as focused ray 240 a. In addition, an incidentray 241 incident inside the outer periphery of the intermediate phaseplate 220 is schematically split into two rays, a focused ray 241 adirected to the first focus F201 and focused ray 241 b directed to thesecond focus F202. Similarly, an incident ray 242 incident inside theouter periphery of the multifocal phase plate 212 is schematically splitinto two rays, a focused ray 242 a directed to the first focus F201 andfocused ray 242 b directed to the second focus F202. As will beappreciated, the rays 240 a, 241 a,b and 242 a,b are representative ofvarious loci of rays produced by the multifocal phase plate 212, theintermediate phase plate 220, and the monofocal phase plate 214. Forexample, the focused ray 240 a belongs to a locus of rays 244 acorresponding to all rays incident just within the outer periphery ofthe intermediate phase plate 220 that are then directed to the firstfocus F201. Similarly, the focused rays 241 a, 241 b, 242 a, and 242 bbelong to loci of rays 246 a, 246 b, 248 a, and 248 b, respectively.

Referring to FIG. 12, a front view of the image plane 238 of FIG. 11 isshown illustrating the intersection of the loci of rays 242 a, 244 a,244 b, 246 a, 246 b with the image plane 238. A filled circle 250represents the intersection of the image plane 238 with the loci of rays244 a, 246 a, and 248 a, since light form these rays are focused ontothe image plane 238. Circles 252 and 254 represent the intersection ofthe image plane 238 with the loci of rays 246 b and 248 b, respectively.Light contained within the circles 252, 254 (apart from that containedin the filled circle 250) contributes to the formation of a halo imageof the type commonly associated with multifocal ophthalmic lenses. Uponinspection of FIGS. 11 and 12, it will be appreciated that, in certainembodiments, light incident upon the intermediate phase plate 220 willbe substantially located between the circles 252, 254, while lightincident upon the multifocal phase plate 212 will be substantiallylocated inside the circle 254. This will be true to the extent thatlight incident upon the phase plates 212, 220 acts in accordance to thegeometric optical representations illustrated in FIGS. 11 and 12. Thatis, when a full physical optics representation of the ophthalmic lens200 is used, it will be appreciated that some light will scatteredoutside the regions just stated. Similarly, it will be appreciated thatsome light will scattered outside the regions just stated when lightfrom an extended source is used.

Embodiments of the present invention have resulted from the recognitionthat the shape of a halo image may have an effect on the perceived levelof disturbance caused by such halos. In light of this recognition, ithas been found that an intermediate phase plate such as the intermediatephase plate 220 may be advantageously configured to change the overallresultant amplitude and/or distribution of light directed to the secondfocus F202, thereby mitigating the level of disturbance generallyassociated with halo images. At least one method of accomplishing thisbenefit is to adjust the amount of energy going into, for example,zeroth and first diffraction orders by forming a phase plate having agrating step height h_(step) that is different from that given byEquation 1 (i.e., a λ/2 phase plate). In one embodiment, the multifocalphase plate 212 is a λ/2 phase plate, the monofocal phase plate 214 is a1λ phase plate, and the intermediate phase plate 220 is configured suchthat,

$\begin{matrix}{{h_{step} = \frac{\lambda}{4\left( {n_{IOL} - n_{o}} \right)}},} & (4)\end{matrix}$herein referred to as a λ/4 phase plate. In such embodiments, about 10%of the available energy transmitted through the intermediate phase plate220 goes into the first diffraction order and about 80% of the availableenergy goes into the zeroth diffraction order.

Referring to FIGS. 13 and 14, potential benefits in configuring theintermediate phase plate 220 as, for example, a λ/4 phase plate will nowbe discussed. FIG. 13 is a graphical representation of intensityprofiles along the cross-section 13-13 in FIG. 12 and is a plot ofintensity verses distance from the optical axis 208. The intensityprofiles shown may be obtained by plotting the intensity along thecross-section 13-13 of (1) focused light within the solid circle 250produced by monofocal phases plate 214 and the zeroth diffraction ordersof the phase plates 212, 220 (I_(focused)), (2) light contributing tothe halo image contained within the circle 252 and produced by the firstdiffraction order of the intermediate phase plate 220(I_(halo, intermediate)), and (3) light contributing to the halo imagecontained within the circle 254 and produced by the first diffractionorder of the multifocal phase plate 220 (I_(halo, multifocal)). Theplots in FIG. 13 are based on a geometric optics approximation in whichlight may be represented as rays, as illustrated in FIG. 11, forexample.

FIG. 14 is a representation of intensity profiles resulting from lightfrom a distant light source (either a point source or extended source)based on a physical optics treatment in which the diffractive effectsof, for example, the finite apertures of the phase plates 212, 214, 220are taken into account. The plot in FIG. 14 also takes into account theeffects produced by an extended source and of dispersion resulting froma source containing light over a broad spectrum and not simply at thedesign wavelength λ. In these plots, I_(halo) contains the combinedeffect of the first diffraction orders produced by the multifocal phaseplate 212 and the intermediate phase plate 220 that contribute to thehalo image. The addition of I_(focused) and I_(halo) is illustrated inFIG. 15, where I_(focused) now represents the portion of the intensityplot dominated by zeroth diffraction order light and I_(halo) representsthe portion of the intensity plot dominated by first diffraction orderlight coming from the multifocal phase plate 212 and the intermediatephase plate 220. It will be appreciated that these plots are notnecessarily to scale. For example, the maximum peak intensity I_(max) isgenerally at least about an order of magnitude higher than theintensities found in the I_(halo) portion of the plot. It will also beappreciated that peripheral portions of the plot I_(halo) aresignificantly sloped. It has been found that halo images with this typeof sloped-periphery intensity profile are generally less noticeable by asubject and may, therefore, be better tolerated than those produced, forexample, by the profile illustrated in FIG. 16 in which there is arelatively sharp cut-off in the intensity at the periphery (somerounding of the peripheral portions of I_(halo) are caused by physicaloptics and light dispersion effects). The profile illustrated in FIG. 16has been found to be typical of ophthalmic lenses in which there is nointermediate phase plate (e.g., an IOL having multifocal phase plateacross the entire optic region or an IOL in which (1) a central portionof the IOL comprises a bifocal λ/2 phase plate and (2) a peripheralportion comprises either a monofocal 1λ phase plate or simply arefractive zone with no diffractive phase plate).

In certain embodiments, the intermediate zone plate 220 of theophthalmic lens 200 comprises two or more echelettes 230 having the sameheight along the optical axis. For example, the number of echelettes 230having the same height may be 3 echelettes to 5 or more echelettes, witha larger number of echelettes 230 being favored in cases where betterdiffractive performance is desired and a smaller number of echelettes230 being favored in cases where a smaller outer diameter for theintermediate zone 220 is favored. Referring to FIG. 17, for example, theintermediate zone plate 220 may comprise 4 echelettes each having aphase step between echelettes 230 of λ/4. FIG. 17 also illustrates someof the echelettes 230 of the multifocal phase plate 212 and themonofocal phase plate 214 disposed near the intermediate zone plate 220.In the illustrated embodiment shown in FIG. 17, the echelettes 230 ofthe intermediate phase plate 220 are disposed on the base curvature C203in such a way that they are centered about the base curvature C203 in adirection that is parallel to the optical axis 208 (see FIG. 11). Insimilar fashion, the echelettes 230 of the phase plates 212, 214 aredisposed on the base curvatures C201, C202, respectively, such that theyare centered about the base curvatures C201, C202 in a direction that isparallel to the optical axis 208. It has been found that thisarrangement of the echelettes 230 of the phase plates 212, 214, 220maintains a consistent phase relationship over the entire surface uponwhich the phase plates are placed (e.g., the anterior surface 204illustrated in FIG. 17). These types of phase considerations arediscussed by Cohen in U.S. Pat. No. 4,881,805. In certain embodiments,the desired phase relationship between the phase plates 212, 214, 220 ismaintained by varying the step size between adjacent zone plates asindicated in FIG. 17. For example, the phase step height betweenadjacent echelettes 230, along with the phase height of the echelettealong the optical axis 208, is λ/2 for the multifocal phase plate 212and λ/4 for the intermediate phase plate 220. However, in order tomaintain the desired phase relationship between phase plates, the phasestep height between a last echelette 258 of the multifocal phase plate212 and a first echelette 260 of the intermediate phase plate 220 isadjusted to 3λ/8. Similarly, as also illustrated in FIG. 17, a 5λ/8phase step height is used between the intermediate phase plate 220 andthe monofocal phase plate 214. By contrast, FIG. 1D of U.S. Pat. No.5,699,142 centers the steps between echelettes on a base curve ratherthan centering the surface of the echelette itself about the base curve,as seen in FIG. 17 of the present embodiment.

In other embodiments, the intermediate phase plate 220 comprises 3, 4, 5or more echelettes 230 having phase heights of 3λ/4 each. Such anarrangement of the echelettes 230 may be used to increase the amount ofenergy into the first diffraction order. This configuration may be usedto increase the amount of energy in the second focus F202, therebyproducing an intensity profile along the cross-section 13-13 in whichthe intensity at the peripheral edges is higher than the intensityprofile closer to the optical axis 208. In general, any number ofechelettes having any predetermined phase height between echelettes maybe used to provide a predetermined distribution of energy between two ormore diffraction orders and, therefore, a predetermined effect on theintensity profile produced by a halo.

In certain embodiments, such alterations to the intensity profile may beused to induce or cause the eye to favor a predetermined pupil diameter,for example, as discussed by Griffin in U.S. Pat. No. 6,474,814, hereinincorporated by reference. Alternatively or additionally, the radius ofcurvature or some other parameter of the second base curvature C202 maybe modified to redirect energy into the first focus F201 or some otherfocus, such as an intermediate focus disposed between the first focusF201 and the second focus F202.

In still other embodiments, the intermediate phase plate 220 comprisestwo echelettes 230 having one phase height disposed nearer themultifocal phase plate 212 and two echelettes 230 having a differentphase height disposed nearer the monofocal phase plate 214. For example,the intermediate phase plate 220 may comprise two echelettes 230 havingphase heights of 3λ/8 located proximal the multifocal phase plate 212and two echelettes 230 having phase heights of λ/8 located proximal themonofocal phase plate 214. Such staggering of the echelettes of theintermediate phase plate 220 may be used to further modify the slope ofthe peripheral edges of the intensity profile shown in FIGS. 14 and 15.

Referring to FIG. 18, in certain embodiments, an ophthalmic lens 300comprises an optic 302 having an anterior surface 304, a posteriorsurface 306, and an optical axis 308. The ophthalmic lens 300 furthercomprises a multifocal phase plate 312 configured to direct light to afirst focus F301 and a second focus F302, an outer refractive region 314having a refractive optical power and no diffractive optical power, andan intermediate phase plate 320 surrounding the inner phase plate 312and configured to change the overall resultant amplitude and/ordistribution of light directed to the second focus F302. The multifocalphase plate 312 comprises a first plurality 321 of echelettes 330disposed about a first base curvature C301 that may have a radius ofcurvature R301 (not shown). The outer refractive region 314 surroundsthe intermediate phase plate 320 and is configured to direct light to athird focus F303 and/or to the first focus F301. The intermediate phaseplate 320 comprises a second plurality 322 of echelettes 330 disposedabout the first base curvature C301 or about a second base curvatureC302. It will be appreciated that the various design parametersavailable for embodiments of the ophthalmic lens 100 illustrated inanyone of FIGS. 3-17 may, when appropriate, also be incorporated intoembodiments of ophthalmic lens 200.

In certain embodiments, the outer refractive region 314 may beconfigured to be disposed on a third base curvature C303 that isdifferent from that of the first base curvature C301 of the multifocalphase plate 312. For example, outer refractive region 314 may bedisposed on a third base curvature C303 having a radius of curvatureselected to direct incident light to the second focus F302 rather thanthe first focus F301, for instance, in order to make the ophthalmic lensmore near vision dominant when the pupil of the eye is larger.Alternatively, third base curvature C303 may have a radius of curvaturethe is configured to direct light to a focus F303 that is between thefirst and second foci F301, F302, or some other location on or off ofthe optical axis 308. Besides having a different radius of curvature,the outer refractive region 314 may alternatively or additionally beshaped differently from the shape of the base curvature C301. Forexample the outer refractive region 314 may have an aspheric shapeconfigured to reduce an optical aberration, such as a sphericalaberration. Alternatively, the outer refractive region 314 may beconfigured to be a multifocal or bifocal lens having more than oneradius of curvature.

In certain embodiments, the echelettes 330 of the intermediate phaseplate 320 are configured to have a zeroth diffraction order that directssome incident light to the first focus F301 and a first diffractionorder that directs some incident light to the second focus F302.Referring to FIG. 19, the intermediate phase plate 320 may be configuredwith a plurality of echelettes 330 (for example, the four echelettes ofthe illustrated embodiment) having a phase height of λ/4, so that onlyabout 10% of light incident on the intermediate phase plate 320 isdirected to the second focus F302. In such embodiments, the reducedamount of light directed to the second focus F302 results in a haloimage about the first focus F301 that has peripheral edges that aresignificantly sloped, thus reducing the disturbance to a subject seeingthe halo image. It will be appreciated that the configurations of theintermediate phase plate 220 of the ophthalmic lens 200 discussed abovemay also be advantageously applied here, with similar results, to theintermediate phase plate 320.

In other embodiments, the second plurality 322 of echelettes 330 formingthe intermediate phase plate 320 may be centered about a third basecurvature C303 having a radius of curvature different from that of thebase curvature C301 or having some other characteristic different fromthat of the base curvature C301. For example, the radius of curvature ofthe third base curvature C303 may be configured to be larger than thatof the first base curvature C301, such that light in the firstdiffraction order of the intermediate phase plate 320 is directed towardthe first focus F301 instead of second focus F302. Alternatively, thebase curvature of the intermediate phase plate 320 may configured with aradius of curvature that is selected to direct light to a focus betweenthe first and second foci F301, F302 or to be otherwise configured toprovide a desired optical effect, such as reducing an aberration of theophthalmic lens 300 or the eye.

The above presents a description of the best mode contemplated ofcarrying out the present invention, and of the manner and process ofmaking and using it, in such full, clear, concise, and exact terms as toenable any person skilled in the art to which it pertains to make anduse this invention. This invention is, however, susceptible tomodifications and alternate constructions from that discussed abovewhich are fully equivalent. Consequently, it is not the intention tolimit this invention to the particular embodiments disclosed. On thecontrary, the intention is to cover modifications and alternateconstructions coming within the spirit and scope of the invention asgenerally expressed by the following claims, which particularly pointout and distinctly claim the subject matter of the invention.

1. An ophthalmic lens, comprising: an optic having an anterior surface,a posterior surface, and an optical axis; a central phase plateconfigured such that the lens is able to direct light to a first focusand a second focus corresponding to different diffraction orders of thephase plate, the central phase plate comprising a first base curvaturehaving a first radius of curvature; an intermediate phase platesurrounding the central phase plate configured to change the overallresultant distribution of light directed to the second focus; and anouter refractive region having no diffractive optical power surroundingthe intermediate phase plate and configured to direct light to thesecond focus, the outer refractive region having an aspheric shapeconfigured to reduce an optical aberration.
 2. The ophthalmic lens ofclaim 1, wherein the optical aberration is a spherical aberration. 3.The ophthalmic lens of claim 1, wherein the phase plates are disposed onthe anterior surface.
 4. The ophthalmic lens of claim 1, wherein theoverall shape of the anterior surface is aspheric.
 5. The ophthalmiclens of claim 4, wherein the overall shape is configured to reduce aspherical aberration.
 6. The ophthalmic lens of claim 4, wherein theoverall shape is configured to reduce spherical aberrations based on anindividual cornea or based on group of corneas.
 7. The ophthalmic lensof claim 1, wherein the overall shape of the posterior surface isaspheric.
 8. The ophthalmic lens of claim 7, wherein the overall shapeis configured to reduce a spherical aberration.
 9. The ophthalmic lensof claim 7, wherein the overall shape is configured to reduce sphericalaberrations based on an individual cornea or based on group of corneas.10. The ophthalmic lens of claim 1, wherein the overall shape of boththe anterior surface and the posterior surface is aspheric.
 11. Theophthalmic lens of claim 1, wherein the optical aberration is anaberration of the ophthalmic lens or the eye.
 12. The ophthalmic lens ofclaim 1, wherein first focus corresponds to a first diffraction order ofthe phase plate and a second focus corresponding to a zeroth diffractionorder of the phase plate.
 13. The ophthalmic lens of claim 1, whereinintermediate phase plate comprises a plurality of different stepheights, the plurality of different step heights progressively decreaseas the distance from the optical axis increases.